Stator core of vehicle rotary electric machine and method of manufacturing the same

ABSTRACT

Each tooth of a stator core has circumferential projections at an inner tooth edge and circumferential notches at a base portion adjacent to a core back. A width of the teeth at the base portion is larger than a width of the same at the tooth edge. Therefore, the magnetic reluctance of the teeth does not increase. In addition, a plurality of the magnetic strips can be formed from a long and thin magnetic sheet. This increases the yield percentage of the magnetic strip and reduces a manpower of manufacturing the magnetic strip. Further, the notches make it easy to wind the magnetic strip into a cylindrical core.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is based on and claims priority fromJapanese Patent Applications: 2000-113966, filed Apr. 14 and2000-359639, filed Nov. 27, 2000; the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a stator core of a vehiclerotary electric machine, such as an AC generator, to be mounted in apassenger car, a truck, etc.

[0004] 2. Description of the Related Art

[0005] In order to supply an inexpensive vehicle rotary machine, amagnetic stator core is usually comprised of a spirally wound magneticstrip. Such a stator core can provide a high yield percentage magneticmaterial and can be manufactured at a high manufacturing speed.

[0006] In order to meet a recent demand for a high power generator,conductors are to be disposed in the slots of the stator core at as ahigh space factor as possible.

[0007] As shown in JP-A11-299136, a pair long and thin magnetic sheetsis stamped out to form a pair of magnetic strips that has a plurality ofteeth and a core back. In order to increase the yield percentage of themagnetic strips, the teeth of one of the pair of magnetic strips arerespectively formed from portions inside slots of the other magneticstrip. Thereafter, each the magnetic strip is spirally wound into acylindrical stack with the slots of one layer being aligned with thoseof another layer until the cylindrical stack has a prescribed thickness.Then, the stack is welded or riveted. Because two or more magneticstrips are formed at one time, the manpower and cost for manufacturingthe stator cores can be reduced.

[0008] In order to moderate stress of a magnetic strip when it isspirally wound, JP-A48-24204 discloses teeth whose tooth width becomesnarrower toward the core back. In other words, slot width is widened atthe middle thereof. This reduces strain of the strip when it is spirallywound and makes the size and shape of a cylindrical stator coreaccurate.

[0009] Because the magnetic reluctance of the air gap between the rotorand the stator is the largest in the magnetic circuit of a generator,the tooth edge formed at the inner periphery of the stator has a widercross-section of a magnetic path than the rest of the tooth. In otherwords, each tooth has a pair of circumferential projections to increasethe width of the tooth.

[0010] As the space factor of the conductors increases, the slot area isnarrowed to thereby widen the cross-section of the tooth. If the teethof one of the pair of magnetic strips are respectively formed fromportions inside slots of the other magnetic strip as disclosed inJP-A-299136, it is not possible to provide such a circumferentially widetooth.

[0011] If the tooth width is narrowed at the middle thereof as shown inJP-A-48-24204, a widened tooth edge of one of a pair of magnetic stripscan be formed from the portion inside a widened slot of the othermagnetic strip. However, if the tooth is narrowed at the middle, themagnetic reluctance of the teeth increases, and the magnetic fluxflowing through the stator core decreases significantly. This lowers theoutput power.

[0012] A stator core of a vehicle AC generator that has an outsidediameter between 90 mm and 140 mm is usually comprised of a laminatedsteel strip of a thickness between 0.5 mm and 1.0 mm. It is necessary tohave a margin (or clearance) if teeth and slots are formed from a steelstrip of the above thickness.

[0013] However, if the thickness is reduced to a thickness less than 0.2mm, the edge of the sheet may be drawn because of the low rigiditythereof. As a result, the projections of the tooth edge can not haveproper length, and a sufficient cross-section of the magnetic flux fromthe rotor can not be provided.

SUMMARY OF THE INVENTION

[0014] Therefore, a main object of the invention is to provide apowerful and inexpensive vehicle rotary electric machine having a statorcore that is free from the above problems.

[0015] In other words, the invention is to provide a stator core of apowerful vehicle rotary machine that can be manufactured at a high yieldpercentage and a high speed.

[0016] In more detail, the invention is to improve the yield percentageof the magnetic strip forming the stator core, to reduce manpower ofmanufacturing the magnetic strip, to reduce the magnetic reluctance ofthe stator core and to improve the space factor of the conductor coils.

[0017] According to a main feature of the invention, each of teeth ofthe stator core has at least a circumferential projection at a toothedge thereof and at least a circumferentially extending notch at a baseportion thereof, and a circumferential width of the teeth at the baseportion is wider than a circumferential width of the teeth at the toothedge from which the circumferential projection extends.

[0018] According to the above structure, the cross-section of the teethat the middle thereof is not narrower than the cross-section at the basethereof. This shape prevents the magnetic reluctance thereof fromincreasing. In addition, it is possible to manufacture a plurality ofmagnetic strips from a long magnetic sheet.

[0019] As a result, the yield percentage of the magnetic strip can beimproved and the manpower for manufacturing the magnetic strip can bereduced. In addition, the magnetic strip can be wound easily because ofthe notches.

[0020] According to another feature of the invention, the notch andprojection are complementary to each other in shape before the magneticstrip is spirally wound, and the radial width of the notch is reducedafter the strip is wound. Therefore, the yield percentage of themagnetic strip is drastically improved. Because the radial width of thenotch is automatically reduced when the magnetic strip is wound, themagnetic reluctance from the teeth to the core back can be reduced.

[0021] According to another feature of the invention, the slot hasparallel walls facing each other in circumferential directions.Therefore, it is easy to align the conductors in the slots, resulting inimprovement of the space factor.

[0022] According to another feature of the invention, the magnetic stripis thicker than 0.2 mm and thinner than 0.5 mm. This thickness makes itpossible to form the magnetic strips with small marginal portions and tostamp out two magnetic strips at once at a reduced cost and prevents thetooth edge from deforming.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other objects, features and characteristics of the presentinvention as well as the functions of related parts of the presentinvention will become clear from a study of the following detaileddescription, the appended claims and the drawings. In the drawings:

[0024]FIG. 1 is a fragmentary enlarged view of an axial end of a statorcore of a vehicle AC generator according to a first embodiment of theinvention;

[0025]FIG. 2 is an explanatory diagram showing a step of manufacturing apair of magnetic strips according to the first embodiment from a longand thin magnetic sheet;

[0026]FIG. 3 is an explanatory diagram showing a step of spirallywinding the magnetic strip according to the first embodiment;

[0027]FIG. 4 is a perspective view of the stator core according to thefirst embodiment;

[0028]FIG. 5 is a fragmentary cross-sectional view of the stator coreaccording to the first embodiment;

[0029]FIG. 6 is a fragmentary cross-sectional view of a stator coreaccording to a variation of the first embodiment of the invention;

[0030]FIG. 7 is an explanatory diagram showing a step of manufacturingmagnetic strips according to a second embodiment of the invention;

[0031]FIG. 8 is an explanatory diagram showing a step of manufacturingmagnetic strips according to a third embodiment of the invention;

[0032]FIG. 9 is a fragmentary cross-sectional view of a stator coreaccording to a fourth embodiment of the invention;

[0033]FIG. 10 is an explanatory diagram showing a step of manufacturingmagnetic strips according to a fifth embodiment of the invention; and

[0034]FIG. 11 is an explanatory diagram showing a step of manufacturingmagnetic strips according to a variation of the fifth embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The invention can be applied to a vehicle rotary electric machinesuch as a generator or a motor. For example, it is mounted in an engineand driven by the engine as an AC generator. It is also mounted in anengine as a motor. Some vehicle AC generators as applications of thevehicle rotary electric machine according to embodiments of theinvention are described with reference to the appended drawings,hereafter.

[0036] A stator core of a vehicle AC generator according to a firstembodiment of the invention is described with reference to FIGS. 1-5.

[0037] A cylindrical stator core 1 is comprised of a spirally wound andlaminated magnetic strip 10 that is as thick as 0.35 mm. The magneticstrip 10 has a plurality of teeth 2 and a core back 3 from which theplurality of teeth 2 extends. When wound and laminated, tooth edges 20of teeth 2 are disposed radially inside, as shown in FIG. 3.

[0038] A plurality of conductor coils 5 is disposed in each slot 6formed between a pair of adjacent teeth 2, as shown in FIG. 5, so thatan electromotive force can be generated in the conductor coils 5 when arotor having a field coil (not shown) supplies an alternating magneticflux. A pair of circumferential notches 21 is formed at opposite sidesof a base portion of each tooth 2 adjacent to the core back 3. A width Bof the base between the notches 21 is set larger than a minimum width Abetween a pair of circumferential projections 201 formed at the toothedge 20. Each slot 6 has a pair of walls 23 and 24 facing each other inthe circumferential direction. The pair of walls 23 and 24 becomesparallel after the magnetic strip 10 is wound up.

[0039] The pair of projections 201 is almost the same in shape as a slotbottom 210 that includes the pair of notches 21. When a pair of magneticstrips 10 is formed from a long and thin magnetic sheet 100 such as ahoop of a steel sheet, the tooth edges 20 of one magnetic strip 10 andthe slot bottom 210 of the other magnetic strip 10 is sheared andseparated without any clearance or margin except for clearances ormarginal portions 200 at opposite sides of each tooth 2, as shown inFIG. 2. This increases the yield percentage of the magnetic strip.Because the thickness of the magnetic strip 10 is 0.35 mm, theprojections 201 do not deform and keep the magnetic reluctance at a lowlevel.

[0040] Thus, the magnetic cross-section of the teeth 2 is the smallestat the base of the projections 201, i.e. at the tooth edge 20 from whichthe projections extend. In other words, the cross-section of middleportion of the teeth 2 between the base of the projections 201 and thecore back 3 is not smaller than the magnetic cross-section at the baseof the projections 201. The radial width of each notch 21 is narrowedwhen the magnetic strip 10 is spirally wound. Accordingly, the magneticreluctance around the notches 21 is reduced when the stator core 1 iscompleted.

[0041] In addition, a plurality of magnetic strips 10 can be formed froma single long and thin magnetic sheet 100, and the notches 21 make thewinding step of the magnetic strip 10 easier.

[0042] Further, the parallel walls 23 and 24 make it easy to align theconductor coils in the slot 6, as shown in FIG. 5 so that a high spacefactor can be provided, resulting in a high power generator. As avariation, the conductor coils can have a rectangular cross-section tobe fitted to the inside walls of each slot 6 including parallel walls,as shown in FIG. 6. This increases the space factor so that more outputpower can be provided.

[0043] As a method of manufacturing the stator core according to asecond embodiment of the invention, a pair of magnetic strips that isoverlapped each other can be stamped as shown in FIG. 7. This stepreduces time of manufacturing magnetic strips 10. It is also possible tostamp out three overlapping magnetic strips at one time. Because thethickness of the magnetic strip 10 is comparatively small, the iron lossof the stator core can be reduced to increase the output power.

[0044] As a method of manufacturing the stator core according to a thirdembodiment of the invention, a long magnetic sheet can be loaded betweena pair of parallel rollers having a punch and a die to stamp out themagnetic strip 10 continuously, as shown in FIG. 8. Because the magneticstrip 10 can be formed continuously, the production time and cost can bereduced.

[0045] The thickness of the magnetic sheets can be changed from 0.35 mmto a thickness between 0.2 mm and 0.5 mm.

[0046] A stator core according to a fourth embodiment of the inventionis described with reference to FIG. 9. A unit of the conductor coils 5can be divided into two groups, and each output power is added to eachother. The number of the slots per each unit length of the magneticsheet becomes twice as many as the number of the slots of the magneticsheet according to the first embodiment. On the other hand the width ofthe slots becomes a half the width of the slot of the magnetic sheetaccording to the first embodiment. Thus, the number of the notchesincreases so that the magnetic strip can be wound into a more accuratecylindrical shape at a low cost.

[0047] As a method of manufacturing the stator core according to a fifthembodiment of the invention, the clearance 200 a for stamping out can beformed at a side of each tooth 2, as shown in FIG. 10. Because the widthof the clearance can be increased, the magnetic strips can be stampedout more easily. The pair of magnetic strips can be formed by the pairof parallel rollers, as shown in FIG. 8.

[0048] As a variation, a clearance 200 can be increased until one of thenotches at the base of the teeth 2 are removed. This makes themanufacturing steps easier and the manufacturing cost lower.

[0049] In the foregoing description of the present invention, theinvention has been disclosed with reference to specific embodimentsthereof. It will, however, be evident that various modifications andchanges may be made to the specific embodiments of the present inventionwithout departing from the scope of the invention as set forth in theappended claims. Accordingly, the description of the present inventionis to be regarded in an illustrative, rather than a restrictive, sense.

What is claimed is:
 1. A stator core of a vehicle rotary electricmachine comprising: a spirally wound magnetic strip having a core backportion, a plurality of teeth extending radially inward from said coreback portion at equal intervals and a plurality of slots formed betweeneach pair of said teeth; wherein each of said teeth comprises at least acircumferential projection at an edge portion thereof and at least acircumferential notch at a base portion thereof, and a circumferentialwidth of said teeth at said base portion is wider than a circumferentialwidth of said teeth at said edge portion from which said circumferentialprojection extends.
 2. The stator core as claimed in claim 1, whereinsaid notch and projection are the same in shape before said magneticstrip is spirally wound, and the width of said notch is reduced aftersaid strip is wound.
 3. The stator core as claimed in claim 1, whereinsaid slot has parallel walls facing each other in circumferentialdirections.
 4. The stator core as claimed in claim 1, wherein saidmagnetic strip is thicker than 0.2 mm and thinner than 0.5 mm.
 5. Astator core of a vehicle rotary electric machine comprising a spirallywound magnetic strip having a plurality of teeth extending radiallyinward at equal intervals and a plurality of slots formed between eachpair of said teeth, wherein each said tooth has a pair ofcircumferential projections at opposite sides of a tooth edge thereofand a pair of circumferential notches at opposite sides of a baseportion thereof, and a circumferential width of said teeth at said baseportion is wider than a circumferential width of said teeth at saidtooth edge from which said pair of circumferential projections projects.6. The stator core as claimed in claim 5, wherein said magnetic strip isthicker than 0.2 mm and thinner than 0.5 mm.
 7. The stator core asclaimed in claim 6, wherein said notch and projection are substantiallycomplementary to each other in shape before said magnetic strip isspirally wound.
 8. The stator core as claimed in claim 7, wherein saidslot has parallel walls facing each other in circumferential directions.9. A method of manufacturing a stator core of a vehicle rotary electricmachine comprising: a step of overlapping two long and thin magneticsheets, and a step of stamping out two magnetic strips having aplurality of teeth and a core back portion from said overlappingmagnetic sheets.
 10. A method of manufacturing a stator core of avehicle rotary electric machine comprising: a step of inserting a longand thin magnetic sheet between a pair of rollers; and a step ofcontinuously stamping out a magnetic strip having a plurality of teethand a core back portion from said sheet by said pair of rollers.
 11. Amethod of manufacturing a stator core of a vehicle rotary electricmachine comprising the steps of: stamping a pair of magnetic stripshaving a plurality of teeth and a plurality of slots from a magneticsheet so that said teeth of one strip are respectively disposed in saidslots of the other; and winding one of said pair of magnetic strip intoa spiral shape so that edges of said teeth are disposed radially inside;wherein said step of stamping comprises a step of forming acircumferential notch at a base of said teeth and a circumferentialprojection at an edge of the same so that said teeth have a shapecomplementary to said slots and a step of forming said base portion ofsaid teeth to have a wider circumferential width than a circumferentialwidth of said teeth at said edge portion thereof from which saidcircumferential projection extends.
 12. The method as claimed in claim11, wherein said step of winding comprises a step of reducing radialwidth of said notches.